The invention relates to a storage coil including a magnetizable core of the type used for flux converters and low setting control elements, and in particular, it relates to a storage coil having a shell core, E core, RM core or U core, with an air gap formed between adjacent end faces of core parts.
Storage coils suitable for flux converters and low settings control elements are required to have a non-linear d-c bias characteristic. At low d-c bias, the inductance should be as high as possible, e.g. 150 uH, and at nominal load, i.e. for instance at 1 to 10 A, much lower, namely e.g. 30 uH. This requirement is not satisfied with ferrite cores with a constant air gap, that is with constant air gap height.
Examples of d-c bias characteristics which may be achieved in this manner are shown in FIG. 3 by the curves a and b respectively for an air gap of small gap height and large gap height or spacing. With a small air gap the inductance is indeed high at low d-c bias, but it decreases rapidly to values of less than 30 mH. With a large air gap height, only inductances of approximately 60 uH are reached at low d-c bias, as shown by the characteristic of curve b.
It is an object of the present invention to provide a storage coil including a magnetizable core which fulfills the stated requirements with respect to the non-linear d-c bias characteristic, at little expense.